Scenario 2: login is successful to HAWQ, however an error "No alive segment" is reported and gprecoverseg is not working? How to bring the cluster up?

If all the segments are down, HAWQ needs to be restarted in order to bring up the segments up.

hawq=# SELECT * FROM pg_catalog.gp_segment_configuration;
ERROR: No alive segment in the GPSQL. (cdbfts.c:1781)
hawq=# \dt
ERROR: No alive segment in the cluser. (cdblink.c:108)
ERROR: No alive segment in the cluser. (cdblink.c:108)
ERROR: No alive segment in the cluser. (cdblink.c:108)

gprecoverseg will not work since it will not be able to start any transactions.